I would recommend the same. However, I once tried to reserve the upper deck at Kuyaba for my wife's birthday and they told me it was first-come-first-served. When we got there, the table was occupied by 4 German girls who stayed there long after they finished dinner, getting drunk. This was a couple years ago, so it might be worth contacting them to see if its now reserve-able.
In addition to Ivan's, we have also enjoyed a special dinner at The Lodge at Tensing Pen.
I agree with you about the Spa Retreat. Had a dinner there last trip - the food was pretty good, but the environment felt sterile.